In order to solve the depletion of fossil energy and global environmental problems caused by the use thereof, research into renewable and clean alternative energy sources such as solar energy, wind power, and water power has been actively conducted.
Of those, an interest in solar cells that can convert from solar light directly into electric energy has significantly increased. Here, the solar cell means a cell that absorbs light energy from solar light and generates a current-voltage by utilizing a photovoltaic effect from which electrons and holes are generated.
Various materials capable of absorbing light energy from solar light to form excitons have been reported. Recently, a perovskite-type compound has been spotlighted. Since it was reported (Scientific Reports 2, 591) that a perovskite-type compound generally has a formula of AMX3 consisting of cations (A and M) and an anion (X) and CH3NH3Pbl3 may be used as an absorber of a solar cell, various compounds have been reported.
Such perovskite compound enables the change of the structure such as the substitution of cations and anions. Through the change of the band gap due to such structure, an absorber suitable for solar cells can be produced. In addition, recently, it has been reported that various electron transport layers and hole transport layers may be used together with a perovskite compound to increase the efficiency of solar cells.
However, the perovskite compound has some limitations in using the same as an absorber of a solar cell. First, the perovskite compound is sensitive to moisture and has problems such as decomposition upon exposure to moisture, thereby causing a disadvantage that it has a poor long-term stability when applied to solar cells. In order to solve this disadvantage, studies have been conducted for substituting the constituent elements of the perovskite compound, but the compounds, which are useful as an absorber of a solar cell while being highly stable against moisture, are significantly limited.
In addition, the perovskite compound has a specific crystal, in which defects tend to occur depending on the preparation conditions. Due to such defects, there is a problem that the efficiency of solar cells is decreased.
Various reactants have been studied to suppress the formation of defects, and recently, an example has been reported in which a DMSO adduct (Pbl2-DMSO) is used as a perovskite precursor (Science 2015, Vol. 348, no. 6240, pp 1234-1237). However, the DMSO adduct (Pbl2-DMSO) is present as Pbl2-DMSO and Pbl2-DMSO2, which causes a problem that the stability of the substance itself is decreased and it is difficult to synthesize the same.
The present inventors have made extensive and intensive studies about a method for preparing a light absorber of a solar cell in which the crystallinity of a perovskite compound is increased, resulting in an increase in the stability and efficiency of the solar cell, and found that the above problems can be solved by the preparation method as described below, thereby completing the present invention.